Various position detection devices detecting the position of the measured object by generating a sine wave (sin θ) signal having a phase (θ) in accordance with the position of the measured object and a cosine wave (cos θ) signal (=another sine wave signal deviated in phase by π/2 relative to the sine wave signal) and detecting phases of those signals are known. For example, a position detection device having an encoder and a position detection device having an amplitude modulation type resolver are known.
Patent Literature 1 discloses the art of calculating a tangent (y=tan θ) from a sine wave signal and a cosine wave signal output from an amplitude modulation type resolver and calculating an arc tangent (θ=tan−1 y) of that tangent to thereby calculate the phase θ.    Patent Document 1: Japanese Patent Publication (A) No. 9-257410